Comparison of the accuracy of optical impression systems in three different clinical situations

Fit and retention of complete denture bases: Part II - conventional impressions versus digital scans: A clinical controlled crossover study

STATEMENT OF PROBLEM

Although the intraoral scanning of edentulous ridges is feasible, clinical evidence that the resulting denture retention is equivalent to that achieved with conventional impressions is lacking.

PURPOSE

The purpose of this clinical study was to determine the retention of complete denture bases fabricated from digital intraoral scans versus conventional impressions by using border molding and posterior palatal seal compression.

MATERIAL AND METHODS

Twenty volunteers with an edentulous maxilla were recruited. An intraoral scan of the maxilla and a conventionally border-molded impression with a custom tray were made. The conventional impression was poured; the definitive cast was scanned. Three-dimensionally (3D) printed (PB1) and milled bases (MB1) were fabricated based on the scan of the definitive cast. Based on the intraoral scan, a 3D printed (PB2) and a milled base (MB2) were fabricated. On each base, a platform with a hook consisting of a central notch orienting the force against the post dam (PD) and 2 lateral notches orienting the forces against the left (LT) and right (RT) tuberosities was set in the center of the outer surface of the base. A traction dynamometer was inserted in the hook and oriented into the corresponding notch by applying force until dislodgement. All bases were subsequently stored in artificial saliva for 2 weeks and scanned. Retention testing was repeated by using the same procedure. To evaluate trueness and to visualize the differences on a color map, the scan of the definitive cast and the intraoral scans were matched and compared in 3 dimensions. The Wilcoxon tests were used to compare the retention of the different bases (95% confidence interval, α=.05).

RESULTS

Nineteen participants with a mean ±standard deviation age of 64.1 ±14.7 years completed the 4 study sessions. The retention of printed bases (PD: 16.08 ±15.28 N; LT: 14.98 ±14.72 N; RT: 11.28 ±9.57 N) and milled bases (PD:14.52 ±17.07 N; RT: 11.99 ±12.10 N; LT: 13.55 ±15.53 N) fabricated from conventional impressions presented significantly higher retentive forces than those printed (PD: 6.21 ±4.72 N; RT:5.12 ±2.78 N; LT: 4.45 ±2.77 N) and milled (PD: 6.58 ±4.92 N; RT: 4.65 ±2.63 N; LT: 5.02 ±3.58 N) from the intraoral scans (P<.05). The differences were significant in all directions of dislodgement, as well as after storage in artificial saliva for 2 weeks. Comparison of the 3D distances between the intraoral scan and the definitive cast revealed a mean deviation of 0.45 ±0.11 mm.

CONCLUSIONS

Conventional impressions of the edentulous maxilla, including the clinical steps of border molding and posterior palatal seal compression, provide better retention than digital intraoral scans with both milled and 3D printed denture bases.

Fit and retention of complete denture bases: Part I - Conventional versus CAD-CAM methods: A clinical controlled crossover study

STATEMENT OF PROBLEM

Clinical evidence is sparse on whether dentures fabricated by computer-aided design and computer-aided manufacturing (CAD-CAM) methods afford superior fit and retention when compared with those fabricated conventionally.

PURPOSE

The purpose of this clinical controlled crossover study was to evaluate the peak retention force and fit of CAD-CAM manufactured (3D printed and milled) maxillary complete denture bases and conventional heat-polymerized bases (control).

MATERIAL AND METHODS

Twenty participants with edentulous maxillary arches were recruited. Impressions were made with a border-molded custom tray, and the resulting definitive cast was scanned. The conventional base was manufactured on the definitive cast with a hook and a 45-degree platform with a central notch and 2 lateral notches. The scan of the definitive cast was used for the fabrication of a milled and a printed base. The platform and hook position on the conventional base were transferred digitally to the milled and printed bases. All bases were scanned. A traction dynamometer was orientated into the notches, and retention was evaluated in the post dam and tuberosity areas. Scans were imported into a comparison software program which matched scans to their corresponding reference and performed a 3-dimensional comparison. The Friedman and Wilcoxon tests were used to compare between groups (confidence interval: 95%, α=.05).

RESULTS

Nineteen participants with a mean ±standard deviation age of 64.1 ±14.7 years completed all clinical sessions. No significant difference in peak retention was measured between milled (MB1), printed (PB1), and conventional (CB) bases in the post dam (CB: 12.44 ±9.62 N, PB1: 16.08 ±15.28 N, MB1: 14.52 ±17.07 N) and right tuberosity area (CB: 8.99 ±7.82 N, PB1: 11.28 ±9.57 N, MB1: 11.99 ±12.10 N). In the left tuberosity area, peak retention was lower for CB (10.03 ±8.39 N) than PB1 (14.98 ±14.72 N) and MB1 (13.55 ±15.53 N; P=.05). Compared with the definitive cast, the fit of the conventional base (0.18 ±0.01 mm) was closer than the printed (0.21 ±0.03 mm) and milled bases (0.21 ±0.02 mm) (P<.001).

CONCLUSIONS

The CD bases manufactured by CAD-CAM techniques provided retention and fit similar to that of conventionally manufactured bases and can therefore be considered suitable techniques.

Influence of age, training, intraoral scanner, and software version on the scan accuracy of inexperienced operators

PURPOSE

To evaluate the effect of operator age on the scan accuracy (trueness and precision) of inexperienced operators when compared with experienced operators, and how training, intraoral scanner (IOS), and software version affect scan accuracy.

MATERIAL AND METHODS

Thirty-four operators were sorted into groups: G1 (operators <25 years old, no experience), G2 (operators >40 years old, no experience), and G3 (experienced IOS operators). They conducted partial-arch scans before and after a 4-session training with two IOSs (Trios 3 and True Definition) and two software versions. These scans were compared with the reference scans obtained from conventional impressions and a laboratory scanner (IScan D103i) to evaluate trueness (mean root mean square values) and precision (standard deviation of root mean square values) with a software program (Geomagic Control X). Kruskal-Wallis and post-hoc Dunn's tests were used to evaluate the effect of age on the scan accuracy of inexperienced groups when compared with experienced operators, while the effect of training, IOS, and software version on scan accuracy was evaluated with Wilcoxon or Mann-Whitney U tests (α = 0.05).

RESULTS

Before training, G1 and G2 scans had similar accuracy (p ≥ 0.065). After training, G1 scans had higher accuracy when IOS data was pooled and had higher precision with TD (p ≤ 0.004). Training increased the scan accuracy (p < 0.001), while newer software increased the trueness of inexperienced operator scans (p = 0.015).

CONCLUSIONS

Age affected the scan accuracy of inexperienced operators after training, indicating that extended training may be required for older operators. Training increased the scan accuracy, and newer software increased the trueness of inexperienced operator scans.

Effect of splinting scan bodies on the trueness of complete-arch digital implant scans with 5 different intraoral scanners

STATEMENT OF PROBLEM

The absence of fixed reference points can affect the trueness of complete-arch intraoral digital implant scans. The effect of splinting intraoral scan bodies (ISBs) or the inclusion of artificial landmarks (AL) on the trueness of complete-arch digital implant scans is still unclear.

PURPOSE

The purpose of this study was to analyze the effect of splinting ISBs or the inclusion of AL on the trueness of complete-arch digital implant scans with 5 intraoral scanners (IOSs).

MATERIAL AND METHODS

Six tissue-level dental implants (Straumann Tissue Level) were placed in an edentulous patient, and the correspondent definitive cast was digitized with a desktop scanner (IScan4D LS3i) to obtain the reference digital cast. Digital scans (n=10) were performed with 5 IOSs: TRIOS 4, Virtuo Vivo, Medit i700, iTero Element 5D, and Cerec Primescan. Three different scanning techniques were evaluated: conventional (cIOSs), splinted (sIOSs), and AL (AL-IOSs). The scan data obtained were imported into a metrology software program and superimposed to the reference digital cast by using a best-fit algorithm. The overall deviations of the positions of the ISBs were evaluated by using the root-mean-square (RMS) error (α=.05).

RESULTS

The mean ±standard deviation trueness values for the cIOSs, sIOSs, and AL-IOSs groups were 48 ±8 µm, 53 ±7 µm, and 49 ±11 µm, respectively, with no statistically significant differences (P=.06). Significant differences were found for the IOSs used with each technique (P<.001). Primescan (27 ±4 µm cIOSs; 28 ±3 µm sIOSs; 31 ±3 µm AL-IOSs) showed significantly higher trueness than iTero 5D (47 ±5 µm cIOSs; 47 ±4 µm sIOSs; 50 ±6 µm AL-IOSs) (P=.002) and TRIOS 4 (93 ±18 µm cIOSs; 76 ±18 µm sIOSs; 107 ±13 µm AL-IOSs) (P=.001) for all techniques. In addition, no significant differences were found between the techniques by using iTero 5D or Primescan (P=.348 and P=.059, respectively).

CONCLUSIONS

The cIOSs, sIOSs, and AL-IOSs techniques showed similar trueness. The IOS used influenced the trueness of complete-arch digital implant scans.

Accuracy of commercial 3D printers for the fabrication of surgical guides in dental implantology

OBJECTIVES

To evaluate the accuracy of two different surgical guides (small extent = single implant and large extent = full arch) fabricated by five additive manufacturing technologies (SLA=Stereolithography, DLP= Digital Light Processing, FDM=Fused Deposition Modeling, SLS=Selective Laser Sintering, Inkjet).

METHODS

Overall, 72 guides (6 per type) were obtained with the different machines (SLA=Form2; DLP=Rapid Shape D40 and Cara Print 4.0; FDM=Raise 3D Pro2; SLS=Prodways P1000; Polyjet®=Stratasys J750). The guides were surface-scanned with an optical dental scanner, and the resulting files were compared with the initial design files using a surface matching software. Root Mean Square (RMS) and standard deviation were calculated, representing respectively trueness and precision. Kruskall-Wallis non-parametric test was used to compare trueness and precision between small-extent and large-extent guides and 3D printer by pairs. The threshold for significance was α=0.05, except for the comparison of printers by pairs where a Bonferroni-corrected level of 0.0033 was used.

RESULTS

Significant differences were observed for trueness and precision between small-extent and large-extent guides, regardless the printer except for DLP (trueness and precision) and SLS (precision). SLA, DLP and Polyjet® technologies showed similar results in terms of trueness and precision for both small-extend and large-extend guides (P>0.05).

CONCLUSIONS

The size affected the accuracy of CAD-CAM surgical guides. The different additive manufacturing technologies had a limited impact on the accuracy.

CLINICAL SIGNIFICANCE

This study is of clinical interest as it shows that the 3D printing technology (SLA/DLP) has a limited impact on 3D printed surgical guides accuracy. However, the size of the guide can have a significant impact, as small-extent guides were more accurate than large-extent guides.